Solid oxide fuel cells (SOFCs) are well known in the art. A typical SOFC comprises a structural, planar anode that is supportive of a thin electrolyte and a thin cathode in an integral multi-layer structure. In use of such an SOFC, oxygen ion migrates through the cathode and electrolyte to react with hydrogen (and other fuels such as CO) in the anode, producing a useful voltage difference and thereby causing current to flow through an external circuit.
A typical prior art SOFC may comprise, for example, Ni-anode supported planar technology using a perovskite oxide such as La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) as the cathode, an oxygen ion conducting yttria stabilized zirconia (YSZ) as the electrolyte, and a nickel-YSZ cermet as the anode.
An LSCF cathode imposes significant material limitations and problems because cathode polarization or resistance is the major source of voltage loss in SOFCs. Therefore, it is desirable to find a catalyst treatment that reduces cathode polarization or resistance during the oxygen reduction reactions occurring in the cathode. In Haanappel et al. (V. A. C. Haanappel, D. Rutenbeck, A. Mai, S. Uhlenbruck, D. Sebold, H. Wesemeyer, B. Rowekamp, C. Tropartz, and F. Tietz, “The Influence of Noble Metal-Containing Cathodes on the Electrochemical Performance of Anode-Supported SOFCs,” J. Power Source, 130 119, 2004), which is incorporated herein by reference, the influence of noble metals, such as Pt, Pd, and Ag, on the performance of perovskite SOFC cathodes, i.e., La0.65Sro0.33MnO3 (LSM) and La0.6Sr0.4Co0.2Fe0.8O3 (LSCF), is investigated. Silver is an attractive choice because of its relatively low price as compared to platinum and palladium. However, the performance of cathodes sintered at 920° C. with Ag powder and Ag20 was inferior to that of Ag-free cathodes sintered at the standard temperature (1100° C.). In addition, a detrimental effect was observed when Ag salt precursors such as Ag acetate, Ag citrate, Ag2CO3, and AgNO3 were applied and then sintered to yield Ag°.
What is needed in the art is a method for impregnating Ag into an LSCF or other cathode to improve cathode performance by reducing cathode resistance and increasing cell power density per unit area.
It is a principal object of the present invention to improve cathode performance of an SOFC.
It is a further object of the invention to provide such improvement economically through use of Ag rather than a more costly noble metal.